Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

207
FXUS63 KLOT 091128
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
628 AM CDT Thu Apr 9 2026

.KEY MESSAGES...

- Less windy and still mild today, with some isolated showers in
  spots.

- Showers and thunderstorms tonight will produce rainfall which
  may exceed an inch north of the Illinois and Kankakee River
  Valleys before tapering to showers and ending Friday morning.
  This could produce new rises on area rivers and creeks.

- Warmer, but more active weather pattern with periods of
  storms returns late in the weekend through early next week.

&&

.DISCUSSION...
Issued at 327 AM CDT Thu Apr 9 2026

Surface low pressure ~1005 mb was analyzed north of Lake
Superior early this morning, with a trailing cold front
extending southwest through WI and northwest IL, then back
across KS to another area of low pressure near the CO/OK/NM
border. A couple of bands of showers were noted along/ahead of
the surface front, within a ~45 kt southwesterly low level jet
axis. Despite the strong southwest flow, low-level moisture is
lacking per 00Z upstream SGF/TOP RAOBs and surface dew points
only in the 40s. SPC/RAP mesoanalysis also indicates little in
the way of MUCAPE within the frontal zone, thus little or no
thunder is expected this morning as these bands of showers
continue to move to the east-southeast ahead of the front. The
front is progged to slow as it shifts south of the I-80 corridor
later this morning/midday and eventually become nearly
stationary in the vicinity of the U.S. 24 corridor (Peoria-
Watseka-Kentland) later this afternoon. Forecast soundings
continue to depict dry low-levels and little in the way of
instability along the front, and CAMs generally have a dry look
to them through mid-afternoon.

Farther to the west, another mid-level short wave emerging from
the northern Rockies this morning is forecast to quickly
translate eastward toward the upper Midwest through this
afternoon, inducing renewed low-level southerly flow across the
Plains. This increases forcing into the low/mid-level baroclinic
zone north of the stationary front into IA/western IL toward
evening, expanding showers and thunderstorms back into the
region this evening/overnight. Stronger forcing and moisture
transport is expected to result in greater coverage/intensity of
convective rains north of the surface front, with guidance
generally indicating a swath of ~1.00+" of QPF across roughly
the northern 2/3 of the forecast area. Ensemble probabilities
currently stand in the 20-40% range of reaching/exceeding an
inch of rainfall. WPC has included this area in a marginal risk
(level 1 of 4) their Day 1 Excessive Rainfall Outlook (ERO), and
if confidence in 1.00"+ amounts continues to increase today may
need to consider a Flood Watch for tonight into early Friday
given recent heavy rains.

The aforementioned short wave eventually tracks east of the
area Friday morning, with the front then pushing south as a cold
front again in the wake of an associated surface low pressure
wave. Shower coverage should decrease in intensity and coverage
while shifting southeast of the area by mid-late morning.
Seasonably strong (~1030 mb) surface high pressure then builds
into the western Great Lakes region Friday afternoon and night,
providing a brief period of dry and cooler weather.

Global models/ensembles remain in good agreement in the upper
level pattern becoming more amplified as we head into the
weekend, in the form of a deep upper trough and closed low
developing over the West Coast downstream ridging across the
Gulf/eastern CONUS. Locally, the surface high pressure over the
area Friday night shifts east on Saturday, allowing low-level
flow to become southeasterly during the day, with temperatures
moderating back into the 60s (except where onshore winds
maintain cooler temps along the IL Lake Michigan shore). Broad
warm/moist advection, tapping low-level moisture from the
western Gulf, then ramps up Saturday night into Sunday
downstream of surface low pressure which lifts from the Plains
into the upper Midwest. Warmer (70s/80s temps) and more humid
(dewpoints into the 60s) weather, combined with a series of mid-
level short wave disturbances riding the fast southwest flow
downstream of the western CONUS upper trough look to provide
periods of active stormy weather into early next week.

Ratzer

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 628 AM CDT Thu Apr 9 2026

Key Aviation Messages for the current TAF period:

- Widespread chances for rain are expected across the region
  tonight. Embedded thunder is possible, but the chance is too
  low for mention in the TAF.

- Wind shift to the northeast late this afternoon/evening, but
  confidence in timing is low.

- IFR cigs possible with the heaviest downpours after
  05Z, then lingering into Friday morning.

Lingering showers are passing over the airspace ahead of a
front. However, with the amount of low level dry air, it is no
surprise that no obs are reporting precip. Still, sprinkles are
possible through mid morning as the front sags south and stalls,
but no impacts are expected. Otherwise VFR conditions and west
southwest winds up to 10 knots are forecasted through the early
afternoon.

As a wave moves northeastward out of the Plains, the stalled
front will begin to lift northward. There is a chance for an
initial wave of rain around or just before 00Z, then rain
chances increase as more moisture surges north overnight. The
threat for thunder is a bit more limited. Models are keeping the
MUCAPE access south of the TAF sites. Embedded thunder is
possible with the rain overnight, but the probability remains
less than 30 percent and therefore left out of the TAFs. One
bit of uncertainty during this renewed rain threat tonight are
wind directions. Previous model runs suggested a lake breeze
developing (and switching winds to the northeast) around or
after 22Z, but have since drifted away from that projection.
However, the large scale wind directions are expected to switch
to the northeast with the heavier rain after 00Z. For now, the
TAFs kept a wind shift to the northeast with the initial wave of
rain, but confidence is low with better confidence in northeast
winds after 02Z. Lastly, as the heavier rains move in
overnight, IFR conditions are expected with heavy rain rates
and lower cigs. Guidance has been far more bullish recently on
the threat for IFR cigs lingering through Friday mid-morning as
rain tapers off, before lifting to MVFR levels.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 7 AM CDT this morning for the IN
     nearshore waters.

&&

$$

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